The present invention relates to drive systems for operating at least two hydraulically operated devices, and more particularly, to such systems wherein the load on one of the devices is a function of the rate of operation of the other device, or of the vehicle itself.
The present invention could be advantageously utilized in a number of applications, such as a street sweeper, on which one hydraulic motor drives a brush, which sweeps debris onto a conveyor, and the conveyor is driven by the other hydraulic motor. As used herein, and in the appended claims, the term "conveyor" will be understood to mean and include any sort of device, such as a flat-belt conveyor or auger, etc., which can convey or advance a quantity of material, wherein the quantity of material being conveyed determines the "load" on the conveyor. However, the present invention is especially advantageous when used in connection with an unloading auger drive system of a grain combine, and will be described in connection therewith. Unloading auger drive systems for grain combines are illustrated and described in U.S. Pat. Nos. 3,938,683; 3,938,684; and 4,037,745, all of which are incorporated herein by reference. In a typical grain combine, the grain being harvested is collected in a grain tank which must be periodically unloaded. The unloading auger drive system for such combines typically includes a horizontal auger disposed at or near the bottom of the grain tank which transports grain to the lower end of a vertical auger. The function of the horizontal auger is to keep the vertical auger full of grain. The upper end of the vertical auger is typically associated with an unloading auger, through which the grain is fed into a storage compartment of a transport vehicle, such as a truck.
In the typical, prior art, unloading auger drive system of the type illustrated in the above-cited patents, the various augers are normally interconnected by, and driven by, a fairly complex system of clutches, right angle gear boxes, sprockets, and chains. In one commercially available grain combine, the auger drive system is activated by a hydraulically operated cylinder, which applies tension to a belt drive arrangement which, in turn, drives the augers.
Although such auger drive systems have been generally satisfactory in operation, certain problems have persisted. For example, if all of the augers are full of grain, the resulting load on the drive system is excessive, and can stall the drive system. Another problem frequently encountered is damage to the grain when the auger is being driven while the grain is compacted and has nowhere to go. Finally, in order to deal with the problem of overloading of the auger drive system, some combine tanks have been provided with a system of adjustable slats in the bottom of the tank or hopper, which adds substantially to the cost and overall complexity of the combine.
Although it was indicated that operation of the prior art auger drive systems has been generally satisfactory, it has been observed that unloading the top one-half of the grain tank takes substantially less time than unloading the bottom one-half of the tank.